Yet despite that progress, Congress is once again beginning a new session without a single member who openly identifies as atheist, according to a Pew Research Center analysis of the latest CQ Roll Call “Faith on the Hill” survey.

The questionnaire identified only one representative ― Sen. Kyrsten Sinema (D-Ariz.) ― who says she is religiously unaffiliated. Sinema, who has taken issue with the “atheist” label in the past, has been the only openly unaffiliated member of Congress since she was elected to the U.S. House in 2012. (She’s also the first openly bisexual member of the U.S. Senate).

An additional 18 members of the 116th Congress responded “don’t know” or didn’t list a religious faith on the latest questionnaire.

The survey underscores a longstanding lack of political representation among the growing ranks of Americans who say they don’t believe in God, are questioning the existence of a higher power, or simply don’t subscribe to traditional organized religion.

Nearly one-quarter of U.S. adults now consider themselves to be religiously unaffiliated, compared to just 0.2 percent of Congress, or 1 in 535 members, according to Pew. Meanwhile, more than 88 percent of Congress identifies as Christian ― including all but two Republicans, both of whom are Jewish ― compared to just 71 percent of the U.S. public. Overall, the 116th Congress is slightly more religiously diverse than the prior Congress, according to Pew.

This gap in representation has persisted as atheists, nontheists, agnostics and other so-called religious “nones” continue to battle for public acceptance following decades of social and political prejudice toward their views.

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Sen. Kyrsten Sinema (D-Ariz.) participates in a ceremonial swearing-in on January 3, 2019. Rather than use a traditional Bible, she placed her hand on a book from the Library of Congress that contains the texts of the Arizona and U.S. constitutions, a spokesperson said.

The simplest definition of an atheist is a person who doesn’t believe in the existence of gods. Ten percent of Americans say they fit that description, according to a 2018 Pew survey. In the current political climate, however, the word “atheist” can be more controversial, often used to hint that someone lacks a moral center or is openly hostile to organized religion.

Amid that cultural backdrop, there have been no open atheists in Congress since 2012, when then-Rep. Pete Stark (D-Calif.) lost his seat to a challenger. Stark had already been in Congress for over three decades when he publicly acknowledged his nonbeliever status in 2007. Former Rep. Barney Frank (D-Mass.) also waited until after he’d retired to announce that he doesn’t believe in God. No candidate has ever entered Congress as an avowed atheist.

The absence of openly atheist representation in the highest ranks of government presents a problem for the religiously unaffiliated, said Roy Speckhardt, executive director of the American Humanist Association (AHA), a nonprofit that promotes the philosophy that people can be good without a god.

“It’s critically important to see ourselves reflected in those who represent us,” said Speckhardt. “When that isn’t the case, it’s very much like a billboard for minorities who are underrepresented, whoever they are.”

But Speckhardt also called into question the accuracy of the latest “Faith on the Hill” survey. He noted that Rep. Jared Huffman (D-Calif.) has publicly questioned the existence of God and said he embraces the “humanist” label, which holds that one can “lead meaningful, ethical lives capable of adding to the greater good of humanity” without theism or other supernatural beliefs, according to the AHA. Rep. Jamie Raskin (D-Md.), a member of the AHA, has similarly identified as a humanist in the past, though he’s distanced himself from the “atheist” label.

Huffman appears to have responded “don’t know” or otherwise refused to list a religious faith on the “Faith on the Hill” survey. But his office said the data was outdated, and confirmed that Huffman identifies as a “nonreligious humanist.” Raskin, meanwhile, is among the 34 members of Congress who identify as Jewish.

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Rep. Jared Huffman (D-Calif.) has publicly questioned the existence of God and said he embraces the “humanist” label, but in a recent survey, he responded “don’t know” or otherwise refused to list a religious faith.

Whatever terms congressional representatives choose to identify their religious beliefs, it’s clear that the stigma against atheism and lack of religious affiliation in politics is beginning to erode, said Speckhardt.

In 2018, Huffman and Raskin were among the founding members of the Congressional Freethought Caucus. The group’s mission, the founders wrote, is to promote “sound public policy based on reason, science, and moral values, protect the secular character of our government, and champion the value of freedom of thought worldwide.”

In the years ahead, Speckhardt said he hopes Congress will make progress on initiatives of particular importance to nonbelievers, including measures to preserve the separation of church and state and protect the rights of nontheists abroad.

There will be no openly atheist torchbearer helping to lead that charge, at least for now. But it’s only a matter of time before that changes, said Speckhardt.

A recent poll commissioned by the AHA suggested that in safely blue districts, a candidate’s atheism is a nonissue, or even a plus, for a large portion of the electorate.

With some members of Congress likely identifying as religious only to avoid the potential negative repercussions of saying they don’t believe in God, the nonbeliever community must show that it will have the back of any politician who publicly embraces the atheist mantle, said Speckhardt.

“[We have] to point out to them that we would much more appreciate their openness about their deeply held convictions, versus hiding them or lying about them,” he said. “Their integrity and their alliance on issues matters to voters much more than whether they happen to believe in God or not.”

This has been updated to include a response from Rep. Jared Huffman’s office about his beliefs.